Tunable notch filter using feedback through an existing feedback receiver

ABSTRACT

A wireless communication device configured for reducing Tx leakage in a receive signal is described. The wireless communication device includes a transceiver chip. The transceiver chip includes a receiver, a feedback receiver and a transmitter. The wireless communication device also includes a Tx leakage signal reduction module. The Tx leakage signal reduction module reuses the feedback receiver.

CLAIM OF PRIORITY UNDER 35 U.S.C. X119

The present Application for Patent claims priority to ProvisionalApplication No. 61/618,483, entitled “Tunable notch filter usingfeedback through an existing envelope tracking (ET) receiver” filed Mar.30, 2012, and assigned to the assignee hereof and hereby expresslyincorporated by reference herein.

TECHNICAL FIELD

The present disclosure relates generally to wireless devices forcommunication systems. More specifically, the present disclosure relatesto systems and methods for a tunable notch filter using feedback throughan existing feedback receiver.

BACKGROUND

Electronic devices (cellular telephones, wireless modems, computers,digital music players, Global Positioning System units, Personal DigitalAssistants, gaming devices, etc.) have become a part of everyday life.Small computing devices are now placed in everything from automobiles tohousing locks. The complexity of electronic devices has increaseddramatically in the last few years. For example, many electronic deviceshave one or more processors that help control the device, as well as anumber of digital circuits to support the processor and other parts ofthe device.

Electronic devices may transmit and receive wireless signalssimultaneously. Because of the distance between an electronic device anda base station, wireless signals received by the electronic device mayhave considerably less amplitude than wireless signals transmitted bythe electronic device. As such, portions of the transmit signal may leakonto the received signals, reducing the signal quality of the receivedsignals. These leaked transmit signals may be filtered out. However,non-adaptive filters are limited in both the amount of signal removedand the frequency band of the signal removed. Benefits may be realizedby using adaptive filters that adapt to the leakage signal that appearson the received signal.

SUMMARY

A wireless communication device configured for reducing Tx leakage in areceive signal is described. The wireless device includes a transceiverchip. The transceiver chip includes a receiver, a feedback receiver anda transmitter. The transceiver chip also includes a Tx leakage signalreduction module. The Tx leakage signal reduction module reuses thefeedback receiver.

The Tx leakage signal reduction module may include a notch filter thatreduces Tx leakage in the receive signal. The notch filter may belocated on the transceiver chip. The notch filter may be coupled to anoutput of a low noise amplifier that receives the receive signal. Thenotch filter may instead be located off the transceiver chip. The notchfilter may receive the receive signal. An output of the notch filter maybe coupled to an input of a low noise amplifier on the transceiver chip.

The receiver may provide a feedback signal to the feedback receiver. Thefeedback receiver may provide a digital leakage reduction signal to theTx leakage signal reduction module. The digital leakage reduction signalmay tune a notch filter in the Tx leakage signal reduction module tominimize Tx leakage in the receive signal. The notch filter may includea first variable capacitor, a second variable capacitor, a firstresistor, a second resistor and an inductor. The notch filter may betuned to provide reliable rejection of Tx leakage across process,voltage and temperature. The digital leakage reduction signal may tune abalancing impedance in a hybrid transformer on the wirelesscommunication device.

The hybrid transformer may include a first inductor, a second inductorand a third inductor. The balancing impedance may be coupled between thesecond inductor and ground. The feedback signal may be provided to afeedback downconverter in the feedback receiver by a first amplifier ina cascode stage in the receiver. An output of the feedback downconvertermay be coupled to an analog-to-digital converter via a feedback basebandfilter. An output of the analog-to-digital converter may be converted tothe digital leakage reduction signal by a digital signal processor.

A method for reducing Tx leakage in a receive signal is also described.The receive signal is received. The receive signal is processed in areceiver. A feedback signal is provided from the receiver to a feedbackdownconverter. The feedback signal is converted to a digital leakagereduction signal using an analog-to-digital converter and a digitalsignal processor. The digital leakage reduction signal is used to reduceTx leakage in the receive signal.

The feedback signal may be downconverted using the feedbackdownconverter. The downconverted feedback signal may be filtered using afeedback baseband filter. Processing the receive signal in the receivermay include passing the receive signal through a notch filter.

A measured notch frequency of the notch filter may be determined Aprocess error may also be determined A first capacitor code and a secondcapacitor code may be calculated that meet requirements for a channel.The first capacitor code may be applied to the first variable capacitorand the second capacitor code may be applied to the second variablecapacitor.

Determining a measured notch frequency of the notch filter may includeapplying a transmit tone on three different frequencies to the notchfilter, measuring a DC gain through the feedback receiver, calculating agradient and determining the measured notch frequency using a gradientsearch algorithm.

An apparatus for reducing Tx leakage in a receive signal is described.The apparatus includes means for receiving the receive signal. Theapparatus also includes means for processing the receive signal in areceiver. The apparatus further includes means for providing a feedbacksignal from the receiver to a feedback downconverter. The apparatus alsoincludes means for converting the feedback signal to a digital leakagereduction signal. The apparatus further includes means for using thedigital leakage reduction signal to reduce Tx leakage in the receivesignal.

A computer-program product for reducing Tx leakage in a receive signalis also described. The computer-program product includes anon-transitory computer-readable medium having instructions thereon. Theinstructions include code for causing a wireless communication device toreceive the receive signal. The instructions also include code forcausing the wireless communication device to process the receive signalin a receiver. The instructions further include code for causing thewireless communication device to provide a feedback signal from thereceiver to a feedback downconverter. The instructions also include codefor causing the wireless communication device to convert the feedbacksignal to a digital leakage reduction signal using an analog-to-digitalconverter and a digital signal processor. The instructions furtherinclude code for causing the wireless communication device to use thedigital leakage reduction signal to reduce Tx leakage in the receivesignal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a wireless communication device for use in the presentsystems and methods;

FIG. 2 is a flow diagram of a method for minimizing a Tx leakage signalin a primary receive signal;

FIG. 3 is a block diagram illustrating a transceiver chip that includesa Tx leakage signal reduction module;

FIG. 4 is a block diagram illustrating another transceiver chip thatincludes a Tx leakage signal reduction module;

FIG. 5 is a flow diagram of another method for minimizing a Tx leakagesignal in a primary receive signal;

FIG. 6 is a block diagram illustrating Tx leakage signal reduction usingan integrated duplexer;

FIG. 7 is a circuit diagram illustrating a notch filter;

FIG. 8 is a flow diagram of a method for process tuning a notch filter;

FIG. 9 is a flow diagram of a method for finding the measured notchfrequency of a notch filter; and

FIG. 10 illustrates certain components that may be included within awireless communication device.

DETAILED DESCRIPTION

The 3^(rd) Generation Partnership Project (3GPP) is a collaborationbetween groups of telecommunications associations that aims to define aglobally applicable 3^(rd) generation (3G) mobile phone specification.3GPP Long Term Evolution (LTE) is a 3GPP project aimed at improving theUniversal Mobile Telecommunications System (UMTS) mobile phone standard.The 3GPP may define specifications for the next generation of mobilenetworks, mobile systems and mobile devices. In 3GPP LTE, a mobilestation or device may be referred to as a “user equipment” (UE).

3GPP specifications are based on evolved Global System for MobileCommunications (GSM) specifications, which are generally known as theUniversal Mobile Telecommunications System (UMTS). 3GPP standards arestructured as releases. Discussion of 3GPP thus frequently refers to thefunctionality in one release or another. For example, Release 99specifies the first UMTS third generation (3G) networks, incorporating aCDMA air interface. Release 6 integrates operation with wireless localarea networks (LAN) networks and adds High Speed Uplink Packet Access(HSUPA). Release 8 introduces dual downlink carriers and Release 9extends dual carrier operation to uplink for UMTS.

CDMA2000 is a family of 3^(rd) generation (3G) technology standards thatuse code division multiple access (CDMA) to send voice, data andsignaling between wireless devices. CDMA2000 may include CDMA2000 1×,CDMA2000 EV-DO Rev. 0, CDMA2000 EV-DO Rev. A and CDMA2000 EV-DO Rev. B.1× or 1×RTT refers to the core CDMA2000 wireless air interface standard.1× more specifically refers to 1 times Radio Transmission Technology andindicates the same radio frequency (RF) bandwidth as used in IS-95.1×RTT adds 64 additional traffic channels to the forward link. EV-DOrefers to Evolution-Data Optimized. EV-DO is a telecommunicationsstandard for the wireless transmission of data through radio signals.

FIG. 1 shows a wireless communication device 104 for use in the presentsystems and methods. A wireless communication device 104 may also bereferred to as, and may include some or all of the functionality of, aterminal, an access terminal, a user equipment (UE), a subscriber unit,a station, etc. A wireless communication device 104 may be a cellularphone, a personal digital assistant (PDA), a wireless device, a wirelessmodem, a handheld device, a laptop computer, a PC card, compact flash,an external or internal modem, a wireline phone, etc. A wirelesscommunication device 104 may be mobile or stationary. A wirelesscommunication device 104 may communicate with zero, one or multiple basestations on a downlink and/or an uplink at any given moment. Thedownlink (or forward link) refers to the communication link from a basestation to a wireless communication device 104, and the uplink (orreverse link) refers to the communication link from a wirelesscommunication device 104 to a base station. Uplink and downlink mayrefer to the communication link or to the carriers used for thecommunication link.

A wireless communication device 104 may operate in a wirelesscommunication system that includes other wireless devices, such as basestations. A base station is a station that communicates with one or morewireless communication devices 104. A base station may also be referredto as, and may include some or all of the functionality of, an accesspoint, a broadcast transmitter, a Node B, an evolved Node B, etc. Eachbase station provides communication coverage for a particular geographicarea. A base station may provide communication coverage for one or morewireless communication devices 104. The term “cell” can refer to a basestation and/or its coverage area, depending on the context in which theterm is used.

Communications in a wireless communication system (e.g., amultiple-access system) may be achieved through transmissions over awireless link. Such a communication link may be established via asingle-input and single-output (SISO) or a multiple-input andmultiple-output (MIMO) system. A multiple-input and multiple-output(MIMO) system includes transmitter(s) and receiver(s) equipped,respectively, with multiple (NT) transmit antennas and multiple (NR)receive antennas for data transmission. SISO systems are particularinstances of a multiple-input and multiple-output (MIMO) system. Themultiple-input and multiple-output (MIMO) system can provide improvedperformance (e.g., higher throughput, greater capacity or improvedreliability) if the additional dimensionalities created by the multipletransmit and receive antennas are utilized.

The wireless communication system may utilize both single-input andmultiple-output (SIMO) and multiple-input and multiple-output (MIMO).The wireless communication system may be a multiple-access systemcapable of supporting communication with multiple wireless communicationdevices 104 by sharing the available system resources (e.g., bandwidthand transmit power). Examples of such multiple-access systems includecode division multiple access (CDMA) systems, wideband code divisionmultiple access (W-CDMA) systems, time division multiple access (TDMA)systems, frequency division multiple access (FDMA) systems, orthogonalfrequency division multiple access (OFDMA) systems, single-carrierfrequency division multiple access (SC-FDMA) systems, 3^(rd) GenerationPartnership Project (3GPP) Long Term Evolution (LTE) systems and spatialdivision multiple access (SDMA) systems.

The wireless communication device 104 may include a primary antenna 106and a secondary antenna 108. In one configuration, the primary antenna106 may be used for transmitting wireless signals and receiving aprimary signal while the secondary antenna 108 may be used for receivinga secondary signal. Both the primary antenna 106 and the secondaryantenna 108 may be coupled to a transceiver chip 110 on the wirelesscommunication device 104.

The transceiver chip 110 may include a transmitter 112, a primaryreceiver (PRx) 114, a diversity receiver (DRx) 116, a feedback receiver147 and a Tx leakage signal reduction module 118. The Tx leakage signalreduction module include a notch filter or an adjustable impedance. Inone configuration, portions of the Tx leakage signal reduction module118 may be located on the transceiver chip 110 while other portions ofthe Tx leakage signal reduction module 118 may be located off thetransceiver chip 110.

In full duplex systems, wireless devices may transmit and receivesimultaneously. The transmit frequency and the receive frequency may beseparated to prevent interference. Typically, the transmit signalbroadcast by a wireless device has a significantly larger amplitude thanthe signals received by the wireless device. This is due to theattenuation of wireless signals (i.e., received signals have attenuatedduring wireless travel while transmit signals need higher amplitude toensure proper reception). For this reason, transmit signals ofteninterfere with receive signals. The noise from the transmit signal thatinterferes with the receive signal may be referred to as the Tx leakagesignal. It is desirable to reduce or eliminate the Tx leakage signal inthe receive signal. The Tx leakage signal may be removed using filters.The Tx leakage signal reduction module 118 may reduce the amplitude ofthe Tx leakage signal using feedback while simultaneously improving thesecond order intercept point (IIP2) and Rx local oscillator (LO) phasenoise requirements. It is desirable for the Tx leakage signal reductionmodule 118 to reuse an existing feedback receiver. In one configuration,the Tx leakage signal reduction module 118 may improve the second orderintercept point (IIP2) without burning a significant amount of current.

In one configuration, the use of the Tx leakage signal reduction modulemay allow for the elimination of an external diversity surface acousticwave (SAW) filter on the wireless communication device 104. Removing anexternal diversity surface acoustic wave (SAW) filter on the wirelesscommunication device 104 may reduce the cost, size and power consumptionof the wireless communication device 104.

FIG. 2 is a flow diagram of a method 200 for minimizing a Tx leakagesignal in a primary receive signal. The method 200 may be performed by awireless communication device 104. In one configuration, the method 200may be performed by a Tx leakage signal reduction module 118 on atransceiver chip 110 in the wireless communication device 104. Thewireless communication device 104 may receive 202 a receive signal. Thereceive signal may be received by the primary antenna 106. The receivesignal may include the desired receive signal and a Tx leakage signal.

The wireless communication device 104 may process 204 the receive signalin a receiver. In one configuration, the wireless communication device104 may process 204 the receive signal in a primary receiver (PRx) 114or a diversity receiver (DRx) 116. The wireless communication device 104may provide 206 a feedback signal from the receiver to a feedbackdownconverter in a feedback receiver. In one configuration, the feedbacksignal may be output from a cascode stage in the receiver. The wirelesscommunication device 104 may then downconvert 208 the frequency of thefeedback signal using the feedback downconverter in the feedbackreceiver. The wireless communication device 104 may filter 210 thefeedback signal in the feedback receiver. The wireless communicationdevice 104 may then convert 212 the feedback signal to a digital leakagereduction signal using an analog-to-digital converter (ADC) and adigital signal processor (DSP). In one configuration, the digital signalprocessor (DSP) may be located on a modem.

The wireless communication device 104 may apply 214 the digital leakagereduction signal to a Tx leakage signal reduction module 118 to minimizethe Tx leakage signal in the receive signal. For example, the digitalleakage reduction signal may be used to adjust the values of a notchfilter. The notch filter may be part of the receiver. Alternatively, thenotch filter may be located off the transceiver chip 110 on the wirelesscommunication device 104. The notch filter may filter out the Tx leakagesignal prior to the cascode stage. Thus, the configuration of the notchfilter may be adjusted using feedback to minimize the Tx leakage signalin the receive signal. As another example, the digital leakage reductionsignal may be used to adjust a tunable impedance in a hybrid transformeron the wireless communication device 104. Adjusting a tunable impedancein a hybrid transformer is discussed in additional detail below inrelation to FIG. 6. Adjusting the tunable impedance may reduce the Txleakage signal in the wireless signal.

FIG. 3 is a block diagram illustrating a transceiver chip 310 thatincludes a Tx leakage signal reduction module 318. The transceiver chip310 of FIG. 3 may be one configuration of the transceiver chip 110 ofFIG. 1. The transceiver chip 310 may include a transmitter 312, afeedback receiver 347 and a receiver 314. The receiver 314 may be aprimary receiver (PRx) or a diversity receiver (DRx). In oneconfiguration, the feedback receiver 347 may be part of the transmitter312.

The transmitter 312 may receive a Tx inphase/quadrature (I/Q) signal326. The Tx inphase/quadrature (I/Q) signal 326 may be passed through aTx baseband filter (BBF) 324 before being upconverted to a transmitfrequency by an upconverter 322. The upconverted transmit signal maythen be amplified by a drive amplifier (DA) 320 before beingtransmitted. The transmitter 312 may include a phase lock loop (PLL)334, a Tx voltage controlled oscillator (VCO) 332 and a Div stage 330that are used to generate a Tx local oscillator (LO) signal 337. The Txlocal oscillator (LO) signal 337 may be provided to the upconverter 322.

The feedback receiver 347 may be used to regulate the transmitter 312(e.g., to provide periodic feedback about the power levels of thetransmitter 312 to ensure that the transmitter 312 is transmitting withthe proper amount of power). During regular operation, the feedbackreceiver 347 may be off for considerable amounts of time (to savepower). In other words, the feedback receiver 347 may normally be turnedon for short amounts of time to track the power of the transmitter 312and then turned off. Thus, the circuitry in the feedback receiver 347may be reused to tune a notch filter 350. For example, the feedbackbaseband filter (BBF) 342 and the Rx analog-to-digital converter (ADC)344 may be reused to tune the notch filter 350.

The circuitry in the feedback receiver 347 may include a feedback lownoise amplifier (LNA) 336 that receives transmit signals. The output ofthe feedback low noise amplifier (LNA) 336 may be coupled to a feedbackdownconverter 338 that reuses the synthesizer of the transmitter 312.Thus, the feedback downconverter 338 may receive the Tx local oscillator(LO) signal 337. The output of the feedback downconverter 338 may becoupled to a feedback baseband filter (BBF) 342. The feedback basebandfilter (BBF) 342 may output the feedback inphase/quadrature (I/Q) signal354 to the modem. The output of the feedback baseband filter (BBF) 342may also be passed through an analog-to-digital converter (ADC) 344before being provided to the modem (although only one analog-to-digitalconverter (ADC) 344 is shown, two analog-to-digital converters (ADCs)344 may be used, one for the inphase signal and one for the quadraturesignal).

To reuse the feedback receiver 347, the receiver 314 may provide afeedback signal 343 to the feedback downconverter 338. The feedbacksignal 343 may be current that is bled from a cascode stage 348 in a Txleakage signal reduction module 318. For example, the cascode stage 348may include a first amplifier 331 a and a second amplifier 331 b. Theoutput of the first amplifier 331 a may be provided to the feedbackdownconverter 338 as the feedback signal 343. The feedback signal 343may be either a voltage signal or a current signal. In oneconfiguration, the feedback signal 343 may be current bled from acascode stage 348. The output of the second amplifier 331 b may beprovided to a downconverter 351 on the receiver 314 as the amplifiedreceive signal 349. The feedback signal 343 may provide feedback about anotch filter 350 in the Tx leakage signal reduction module 318, allowingthe notch filter 350 to be tuned. The feedback signal 343 may beprocessed by the feedback receiver 347 (via the Rx analog-to-digitalconverter (ADC) 344) to obtain a digital leakage reduction signal 364.Additional digital signal processing (e.g., by the modem) may beperformed on the output of the Rx analog-to-digital converter (ADC) 344(such as by a digital signal processor (DSP)) to obtain the digitalleakage reduction signal 364. The digital leakage reduction signal 364may be used to tune the Tx leakage signal reduction module 318 in thereceiver 314.

The receiver 314 may include a low noise amplifier (LNA) 346. The lownoise amplifier (LNA) 346 may receive a receive signal 345. The receivesignal 345 may include undesirable Tx leakage. To reduce the Tx leakagein the receive signal 345, the primary 314 may include a Tx leakagereduction module 318. The Tx leakage signal reduction module 318 mayinclude the cascode stage 348 and the notch filter 350. The notch filter350 may be coupled to the output of the low noise amplifier (LNA) 346.The notch filter 350 may also receive the digital leakage reductionsignal 364. The digital leakage reduction signal 364 may provideaccurate notch filter 350 tuning across process, voltage and temperature(PVT) to minimize the Tx leakage in the receive signal 345. The Txleakage signal reduction module 318 may use existing hardware (such asthe feedback receiver 347) to reduce the Tx leakage signal (by tuningthe notch filter 350 to remove the Tx leakage signal).

The output of the low noise amplifier (LNA) 346 may be coupled to thenotch filter 350. The output of the notch filter 350 may be coupled tothe cascode stage 348. As discussed above, the cascode stage 348 mayinclude a first amplifier 331 a and a second amplifier 331 b. The outputof the second amplifier may be provided to a downconverter 351 on thereceiver 314. In one configuration, 10% of the current is bled as thefeedback signal 343.

The receiver 314 may include a phase lock loop (PLL) 362, an Rx voltagecontrolled oscillator (VCO) 360 and a Div stage 358 that provide an Rxlocal oscillator (LO) signal 339 to the downconverter 351. Thedownconverter 351 may convert signals to baseband frequency. The outputof the downconverter 351 may be coupled to an Rx baseband filter (BBF)352. The Rx baseband filter (BBF) 352 may then output theinphase/quadrature (I/Q) signal 356. Using the feedback receiver 347 totune the notch filter 350 may provide reliable rejection of the Txleakage signal across process, voltage and temperature (PVT).

FIG. 4 is a block diagram illustrating another transceiver chip 410 thatincludes a Tx leakage signal reduction module 418. The Tx leakage signalreduction module 418 may include a notch filter 450 that is located offthe transceiver chip 410. The transceiver chip 410 of FIG. 4 may be oneconfiguration of the transceiver chip 110 of FIG. 1. The transceiverchip 410 may include a transmitter 412, a feedback receiver 447 and areceiver 414. In one configuration, the feedback receiver 447 may bepart of the transmitter 412. The receiver 414 may be a primary receiver(PRx) or a diversity receiver (DRx).

The transmitter 412 may receive a Tx inphase/quadrature (I/Q) signal426. The Tx inphase/quadrature (I/Q) signal 426 may be passed through aTx baseband filter (BBF) 424 before being upconverted to a transmitfrequency by an upconverter 422. The transmit signal may then beamplified by a drive amplifier (DA) 420 before being transmitted. Thetransmitter 412 may include a phase lock loop (PLL) 434, a Tx voltagecontrolled oscillator (VCO) 432 and a Div stage 430 that are used togenerate a Tx local oscillator (LO) signal 437. The Tx local oscillator(LO) signal 437 may be provided to the upconverter 422.

The feedback receiver 447 may be used to regulate the transmitter 412(e.g., to provide periodic feedback about the power levels of thetransmitter 412 to ensure that the transmitter 412 is transmitting withthe proper amount of power). During regular operation, the feedbackreceiver 447 may be off for considerable amounts of time (to savepower). In other words, the feedback receiver 447 may normally be turnedon for short amounts of time to track the power of the transmitter 412and then turned off Thus, the circuitry in the feedback receiver 447 maybe reused to tune a notch filter 450. Tuning using the feedback receiver447 may be performed only one time or performed periodically, when thefeedback receiver 447 is idle.

The circuitry in the feedback receiver 447 may include a feedback lownoise amplifier (LNA) 436 that receives transmit signals. The output ofthe feedback low noise amplifier (LNA) 436 may be coupled to a feedbackdownconverter 438 that reuses the synthesizer of the transmitter 412.Thus, the feedback downconverter 438 may receive the Tx local oscillator(LO) signal 437. The output of the feedback downconverter 438 may becoupled to a feedback baseband filter (BBF) 442. The feedback basebandfilter (BBF) 442 may output the feedback inphase/quadrature (I/Q) signal454 to the modem. The output of the feedback baseband filter (BBF) 442may also be passed through an analog-to-digital converter (ADC) 444before being provided to the modem.

To reuse the feedback receiver 447, the receiver 414 may provide afeedback signal 443 to the feedback downconverter 438. The feedbacksignal 443 may be current that is bled from a cascode stage 448 in a Txleakage signal reduction module 418. For example, the cascode stage 448may include a first amplifier 431 a and a second amplifier 431 b. Theoutput of the first amplifier 431 a may be provided to the feedbackdownconverter 438 as the feedback signal 443. The output of the secondamplifier 431 b may be provided to a downconverter 451 on the receiver414 as the amplified receive signal 449. The feedback signal 438 mayprovide feedback about a notch filter 450 in the Tx leakage signalreduction module 418, allowing the notch filter 450 to be tuned. Thefeedback signal 443 may be processed by the feedback receiver 447 (viathe Rx analog-to-digital converter (ADC) 444) to obtain a digitalleakage reduction signal 464. Additional digital signal processing(e.g., by the modem) may be performed on the output of the Rxanalog-to-digital converter (ADC) 444 to obtain the digital leakagereduction signal 464. The digital leakage reduction signal 464 may beused to tune the Tx leakage signal reduction module 418 in the receiver414.

The Tx leakage signal reduction module 418 may include a notch filter450. In one configuration, the notch filter 450 may not be located onthe transceiver chip 410 (and thus may be located off-chip). The notchfilter 450 may receive a receive signal 445. The notch filter 450 mayalso receive the digital leakage reduction signal 464 (which tunes thenotch filter 450). The output of the notch filter 450 may be provided tothe cascode stage 448. As discussed above, the cascode stage 448 mayinclude a first amplifier 431 a and a second amplifier 431 b. The outputof the first amplifier 431 a may be the feedback signal 443 provided tothe feedback receiver 447. The output of the second amplifier 431 b maybe the amplified receive signal 349 provided to the downconverter 451.In one configuration, 10% of the current in the cascode stage 448 may bebled as the feedback signal 443.

The digital leakage reduction signal 464 may provide accurate notchfilter 450 tuning across process, voltage and temperature (PVT) tominimize the Tx leakage in the receive signal 445. The Tx leakage signalreduction module 418 may use existing hardware (such as the feedbackreceiver 447) to reduce the Tx leakage signal (by tuning the notchfilter 450 to remove the Tx leakage signal).

The receiver 414 may include a phase lock loop (PLL) 462, an Rx voltagecontrolled oscillator (VCO) 460 and a Div stage 458 that provide an Rxlocal oscillator (LO) signal 439 to the downconverter 451. Thedownconverter 451 may convert signals to baseband frequency. The outputof the downconverter 451 may be coupled to an Rx baseband filter (BBF)452. The Rx baseband filter (BBF) 452 may then output theinphase/quadrature (I/Q) signal 456. Using the feedback receiver 447 totune the notch filter 450 may provide reliable rejection of the Txleakage signal across process, voltage and temperature (PVT).

FIG. 5 is a flow diagram of another method 500 for minimizing a Txleakage signal in a receive signal 345. The method 500 may be performedby a wireless communication device 104. In one configuration, the method500 may be performed by a Tx leakage signal reduction module 318 on atransceiver chip 310 in the wireless communication device 104. Thewireless communication device 104 may receive 502 a receive signal 345.The receive signal 345 may be received by an antenna 106, 108. Thereceive signal 345 may include undesirable Tx leakage.

The wireless communication device 104 may pass 504 the receive signal345 through a notch filter 350. The wireless communication device 104may amplify 506 the receive signal using a cascode stage 348. Thewireless communication device 104 may provide 508 a feedback signal 343from the cascode stage 348 to a feedback receiver 347. The wirelesscommunication device 104 may obtain 510 a digital leakage reductionsignal 364 from the feedback signal 343 using the feedback receiver 347.For example, the feedback signal 343 may be downconverted by a feedbackdownconverter 338, filtered by a feedback baseband filter (BBF) 342 andconverted to a digital signal by an Rx analog-to-digital converter (ADC)344 in the feedback receiver 347.

The wireless communication device 104 may perform 512 process tuning onthe notch filter 350 using the digital leakage reduction signal 364 tominimize Tx leakage in the receive signal 345. For example, the digitalleakage reduction signal 364 may be used to adjust the values of thenotch filter 350 (and thus adjust the frequencies filtered by the notchfilter 350).

FIG. 6 is a block diagram illustrating Tx leakage signal reduction usingan integrated duplexer. The integrated duplexer may be implemented usinga hybrid transformer 670. The hybrid transformer 670 may include a firstinductor L1 666 a, a second inductor L2 666 b and a third inductor L3666 c. A coupling may occur between the first inductor L1 666 a, thesecond inductor L2 666 b and the third inductor L3 666 c. The firstinductor Ll 666 a may be coupled between a primary antenna 606 and thesecond inductor L2 666 b. The second inductor L2 666 b may be coupledbetween the first inductor L1 666 a and a balancing impedance ZL 668.The balancing impedance ZL 668 may also be coupled to ground. The thirdinductor L3 666 c may be coupled to both a first differential input anda second differential input of a low noise amplifier (LNA) 646 on atransceiver chip 610. The low noise amplifier (LNA) 646 may be part of areceiver 614.

The transceiver chip 610 of FIG. 6 may be one configuration of thetransceiver chip 110 of FIG. 1. The transceiver chip 610 may include atransmitter 612, a feedback receiver 647 and the receiver 614. In oneconfiguration, the feedback receiver 647 may be part of the transmitter612. The receiver 614 may be a primary receiver (PRx) or a diversityreceiver (DRx). The transmitter 612 may receive a Tx inphase/quadrature(I/Q) signal 626. The Tx inphase/quadrature (I/Q) signal 626 may bepassed through a Tx baseband filter (BBF) 624 before being upconvertedto a transmit frequency by an upconverter 622. The transmit signal maythen be amplified by a drive amplifier (DA) 620. The output of the driveamplifier (DA) 620 may be coupled to the input of a power amplifier (PA)690. The power amplifier (PA) 690 may be located off the transceiverchip 610. The output of the power amplifier (PA) 690 may be coupledbetween the first inductor L1 666 a and the second inductor L2 666 b.The transmitter 612 may include a phase lock loop (PLL) 634, a Txvoltage controlled oscillator (VCO) 632 and a Div stage 630 that areused to generate a Tx local oscillator (LO) signal 637. The Tx localoscillator (LO) signal 637 may be provided to the upconverter 622.

The feedback receiver 647 may be used to regulate the transmitter 612(e.g., to provide periodic feedback about the power levels of thetransmitter 612 to ensure that the transmitter 612 is transmitting withthe proper amount of power). During regular operation, the feedbackreceiver 647 may be off for considerable amounts of time (to savepower). In other words, the feedback receiver 647 may normally be turnedon for short amounts of time to track the power of the transmitter 612and then turned off. Thus, the circuitry in the feedback receiver 647may be reused to tune the balancing impedance ZL 668. Tuning using thefeedback receiver 447 may be performed only one time or performedperiodically, when the feedback receiver 447 is idle.

The circuitry in the feedback receiver 647 may include a feedback lownoise amplifier (LNA) 636 that receives transmit signals. The output ofthe feedback low noise amplifier (LNA) 436 may be coupled to a feedbackdownconverter 438 that reuses the synthesizer of the transmitter 412.Thus, the feedback downconverter 638 may receive the Tx local oscillator(LO) signal 637. The output of the feedback downconverter 638 may becoupled to a feedback baseband filter (BBF) 642. The feedback basebandfilter (BBF) 642 may output the feedback inphase/quadrature (I/Q) signal654 to the modem. The output of the feedback baseband filter (BBF) 642may also be passed through an analog-to-digital converter (ADC) 644before being provided to the modem.

To reuse the feedback receiver 647, the receiver 614 may provide afeedback signal 643 to the feedback downconverter 638. The feedbacksignal 643 may be current that is bled from a cascode stage 648 in thereceiver 614. For example, the cascode stage 648 may include a firstamplifier 631 a and a second amplifier 631 b. The output of the firstamplifier 631 a may be provided to the feedback downconverter 638 as thefeedback signal 643. The output of the second amplifier 631 b may beprovided to a downconverter 651 on the receiver 614 as the amplifiedreceive signal 649. The feedback signal 638 may provide feedback aboutthe balancing impedance ZL 668 in the hybrid transformer 670, allowingthe balancing impedance ZL 668 to be tuned. The feedback signal 643 maybe processed by the feedback receiver 647 (via the Rx analog-to-digitalconverter (ADC) 644) to obtain a digital leakage reduction signal 664.Additional digital signal processing (e.g., by the modem) may beperformed on the output of the Rx analog-to-digital converter (ADC) 644to obtain the digital leakage reduction signal 664.

The digital leakage reduction signal 664 may be used to tune thebalancing impedance ZL 668 in the hybrid transformer 670. Using thefeedback receiver 647 to tune the balancing impedance ZL 668 may providereliable rejection of the Tx leakage signal across process, voltage andtemperature (PVT). The impedance measured by the primary antenna 606 maybe too course for application in a hybrid transformer 670. By using thebalancing impedance ZL 668, better sensitivity may be obtained.Continuous feedback (via the digital leakage reduction signal 664) maybe used to tune the antenna load.

The output of the low noise amplifier (LNA) 646 may be coupled to theinput of the cascode stage 648. As discussed above, the cascode stage648 may include a first amplifier 631 a and a second amplifier 631 b.The first amplifier 631 a may output the feedback signal 643 to thefeedback receiver 647. The second amplifier 631 b may output theamplified receive signal 649 to a downconverter 651 on the receiver 614.In one configuration, the cascode stage 648 may bleed off 10% of thecurrent to the feedback receiver 647.

The receiver 614 may include a phase lock loop (PLL) 662, an Rx voltagecontrolled oscillator (VCO) 660 and a Div stage 658 that provide an Rxlocal oscillator (LO) signal 639 to the downconverter 651. Thedownconverter 651 may convert signals to baseband frequency. The outputof the downconverter 651 may be coupled to an Rx baseband filter (BBF)652. The Rx baseband filter (BBF) 652 may then output theinphase/quadrature (I/Q) signal 656.

FIG. 7 is a circuit diagram illustrating a notch filter 750. The notchfilter 750 of FIG. 7 may be one configuration of the notch filter 350 ofFIG. 3 or the notch filter 450 of FIG. 4. The notch filter 750 may havean input and an output. The notch filter 750 may include a firstvariable capacitor C1 770 a and a second variable capacitor C2 770 b.The first variable capacitor C1 770 a may be coupled between the secondvariable capacitor C2 770 b and ground. The second variable capacitor C2770 b may be coupled to the input of the notch filter 750.

The notch filter 750 may also include a resistor R1 774 and an inductorL1 772. The resistor R1 774 may be coupled between the inductor L1 772and ground. The inductor L1 772 may be coupled between the resistor R1774 and the second variable capacitor C2 770 b. The notch filter 750 mayalso include a resistor Rneg 776. The resistor Rneg 776 may be coupledbetween ground and the second variable capacitor C2 770 b. The resistorRneg 776 is the equivalent negative resistor of a circuit (such as anegative-gm circuit) that is used to improve the equivalent Qualityfactor (Q) of the inductor L1 772. The Quality factor (Q) of the notchfilter 750 may be found using Equation (1):

$\begin{matrix}{Q = {\left( \frac{\omega_{0}L_{1}}{R_{1}} \right).}} & (1)\end{matrix}$

In Equation (1), ω₀ is the notch frequency of the notch filter 750. Theeffective paddle inductance Lp from the bottom of the capacitor C2 770 bto ground may be found using Equation (2):

$\begin{matrix}{L_{p} = {L_{1} \cdot {\left( \frac{Q^{2} + 1}{Q^{2}} \right).}}} & (2)\end{matrix}$

The passband frequency f_(p) of the notch filter 750 may be found usingEquation (3):

$\begin{matrix}{f_{p} = {\frac{1}{2\pi \sqrt{L_{p} \cdot C_{1}}}.}} & (3)\end{matrix}$

The notch frequency f_(n) of the notch filter 750 may be found usingEquation (4):

$\begin{matrix}{f_{n} = {\frac{1}{2\pi \sqrt{L_{p} \cdot \left( {C_{1} + C_{2}} \right)}}.}} & (4)\end{matrix}$

The value for the first variable capacitor C1 770 a may be found usingEquation (5):

$\begin{matrix}{C_{1} = {\frac{1}{\left( {2{\pi \cdot f_{p}}} \right)^{2} \cdot L_{p}}.}} & (5)\end{matrix}$

Likewise, the value for the second variable capacitor C2 770 b may befound using Equation (6):

$\begin{matrix}{C_{2} = {C_{1} \cdot {\left\lbrack {\left( \frac{f_{p}}{f_{n}} \right)^{2} - 1} \right\rbrack.}}} & (6)\end{matrix}$

The equivalent resistance Rp from the capacitor C2 770 b to ground maybe found using Equation (7):

R _(p) =R ₁·(Q ²+1)∥R _(neg).   (7)

The equivalent resistance Req may be found using Equation (8):

$\begin{matrix}{R_{eq} \approx {R_{p} \cdot {\left( {1 + \frac{C_{1}}{C_{2}}} \right)^{2}.}}} & (8)\end{matrix}$

FIG. 8 is a flow diagram of a method 800 for process tuning a notchfilter 750. The method 800 may be performed by a wireless communicationdevice 104. The wireless communication device 104 may determine 802 ameasured notch frequency. Determining the measured notch frequency isdiscussed in additional detail below in relation to FIG. 9. The measurednotch frequency may be found using Equation (9):

$\begin{matrix}{F_{n,{meas}} = {\frac{1}{2\pi \sqrt{{L_{p} \cdot \left( {1 + \alpha} \right)}\left( {C_{1} + C_{2}} \right)}}.}} & (9)\end{matrix}$

In Equation (9), α is the process error that occurs from the notchfrequency shifting due to process error. The wireless communicationdevice 104 may determine 804 the process error α. The process error amay be determined using Equation (10:

$\begin{matrix}{\alpha = {\left\lbrack {\left( \frac{f_{n}}{f_{n,{meas}}} \right)^{2} - 1} \right\rbrack.}} & (10)\end{matrix}$

The wireless communication device 104 may calculate 806 a firstcapacitor code (i.e., a code that adjusts the value of the firstvariable capacitor Cl 770 a) and a second capacitor code (i.e., a codethat adjusts the value of the second variable capacitor C2 770 b) thatmeets the C₁ _(—) _(aim) and C₂ _(—) _(aim) for a given channel. Thewireless communication device 104 may then apply 808 the first capacitorcode and the second capacitor code to the notch filter 750.

FIG. 9 is a flow diagram of a method 900 for finding the measured notchfrequency of a notch filter 750. The method 900 may be performed by awireless communication device 104. Notch tuning may be performed withany search-efficient algorithm, such as a gradient search algorithm. Thewireless communication device 104 may apply 902 a transmit tone on threedifferent frequencies to the notch filter 750. The wirelesscommunication device 104 may then measure 904 the DC gain through thefeedback receiver 347. The wireless communication device 104 maycalculate 906 the gradient. The wireless communication device 104 maydetermine 908 a notch frequency using a gradient search algorithm. Thenotch frequency found using the gradient search algorithm may havebetter results than a linear search. The steps in the method 900 mayneed to be repeated to precisely locate the notch frequency and finetune the notch filter 750.

FIG. 10 illustrates certain components that may be included within awireless communication device 1004. The wireless communication device1004 may be an access terminal, a mobile station, a user equipment (UE),etc. The wireless communication device 1004 includes a processor 1003.The processor 1003 may be a general purpose single- or multi-chipmicroprocessor (e.g., an ARM), a special purpose microprocessor (e.g., adigital signal processor (DSP)), a microcontroller, a programmable gatearray, etc. The processor 1003 may be referred to as a centralprocessing unit (CPU). Although just a single processor 1003 is shown inthe wireless communication device 1004 of FIG. 10, in an alternativeconfiguration, a combination of processors (e.g., an ARM and DSP) couldbe used.

The wireless communication device 1004 also includes memory 1005. Thememory 1005 may be any electronic component capable of storingelectronic information. The memory 1005 may be embodied as random accessmemory (RAM), read-only memory (ROM), magnetic disk storage media,optical storage media, flash memory devices in RAM, on-board memoryincluded with the processor, EPROM memory, EEPROM memory, registers andso forth, including combinations thereof

Data 1007 a and instructions 1009 a may be stored in the memory 1005.The instructions 1009 a may be executable by the processor 1003 toimplement the methods disclosed herein. Executing the instructions 1009a may involve the use of the data 1007 a that is stored in the memory1005. When the processor 1003 executes the instructions 1009, variousportions of the instructions 1009 b may be loaded onto the processor1003, and various pieces of data 1007 b may be loaded onto the processor1003.

The wireless communication device 1004 may also include a transmitter1011 and a receiver 1013 to allow transmission and reception of signalsto and from the wireless communication device 1004 via a first antenna1017 a and a second antenna 1017 b. The transmitter 1011 and receiver1013 may be collectively referred to as a transceiver 1015. The wirelesscommunication device 1004 may also include (not shown) multipletransmitters, additional antennas, multiple receivers and/or multipletransceivers.

The wireless communication device 1004 may include a digital signalprocessor (DSP) 1021. The wireless communication device 1004 may alsoinclude a communications interface 1023. The communications interface1023 may allow a user to interact with the wireless communication device1004.

The various components of the wireless communication device 1004 may becoupled together by one or more buses, which may include a power bus, acontrol signal bus, a status signal bus, a data bus, etc. For the sakeof clarity, the various buses are illustrated in FIG. 10 as a bus system1019.

The term “determining” encompasses a wide variety of actions and,therefore, “determining” can include calculating, computing, processing,deriving, investigating, looking up (e.g., looking up in a table, adatabase or another data structure), ascertaining and the like. Also,“determining” can include receiving (e.g., receiving information),accessing (e.g., accessing data in a memory) and the like. Also,“determining” can include resolving, selecting, choosing, establishingand the like.

The phrase “based on” does not mean “based only on,” unless expresslyspecified otherwise. In other words, the phrase “based on” describesboth “based only on” and “based at least on.”

The term “processor” should be interpreted broadly to encompass ageneral purpose processor, a central processing unit (CPU), amicroprocessor, a digital signal processor (DSP), a controller, amicrocontroller, a state machine and so forth. Under some circumstances,a “processor” may refer to an application specific integrated circuit(ASIC), a programmable logic device (PLD), a field programmable gatearray (FPGA), etc. The term “processor” may refer to a combination ofprocessing devices, e.g., a combination of a DSP and a microprocessor, aplurality of microprocessors, one or more microprocessors in conjunctionwith a DSP core, or any other such configuration.

The term “memory” should be interpreted broadly to encompass anyelectronic component capable of storing electronic information. The termmemory may refer to various types of processor-readable media such asrandom access memory (RAM), read-only memory (ROM), non-volatile randomaccess memory (NVRAM), programmable read-only memory (PROM), erasableprogrammable read-only memory (EPROM), electrically erasable PROM(EEPROM), flash memory, magnetic or optical data storage, registers,etc. Memory is said to be in electronic communication with a processorif the processor can read information from and/or write information tothe memory. Memory that is integral to a processor is in electroniccommunication with the processor.

The terms “instructions” and “code” should be interpreted broadly toinclude any type of computer-readable statement(s). For example, theterms “instructions” and “code” may refer to one or more programs,routines, sub-routines, functions, procedures, etc. “Instructions” and“code” may comprise a single computer-readable statement or manycomputer-readable statements.

The functions described herein may be implemented in software orfirmware being executed by hardware. The functions may be stored as oneor more instructions on a computer-readable medium. The terms“computer-readable medium” or “computer-program product” refers to anytangible storage medium that can be accessed by a computer or aprocessor. By way of example, and not limitation, a computer-readablemedium may comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage or other magnetic storage devices, or anyother medium that can be used to carry or store desired program code inthe form of instructions or data structures and that can be accessed bya computer. Disk and disc, as used herein, includes compact disc (CD),laser disc, optical disc, digital versatile disc (DVD), floppy disk andBlu-ray® disc where disks usually reproduce data magnetically, whilediscs reproduce data optically with lasers. It should be noted that acomputer-readable medium may be tangible and non-transitory. The term“computer-program product” refers to a computing device or processor incombination with code or instructions (e.g., a “program”) that may beexecuted, processed or computed by the computing device or processor. Asused herein, the term “code” may refer to software, instructions, codeor data that is/are executable by a computing device or processor.

Software or instructions may also be transmitted over a transmissionmedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio and microwave are included in the definition oftransmission medium.

The methods disclosed herein comprise one or more steps or actions forachieving the described method. The method steps and/or actions may beinterchanged with one another without departing from the scope of theclaims. In other words, unless a specific order of steps or actions isrequired for proper operation of the method that is being described, theorder and/or use of specific steps and/or actions may be modifiedwithout departing from the scope of the claims.

Further, it should be appreciated that modules and/or other appropriatemeans for performing the methods and techniques described herein, suchas those illustrated by FIGS. 2, 5, 8 and 9, can be downloaded and/orotherwise obtained by a device. For example, a device may be coupled toa server to facilitate the transfer of means for performing the methodsdescribed herein. Alternatively, various methods described herein can beprovided via a storage means (e.g., random access memory (RAM),read-only memory (ROM), a physical storage medium such as a compact disc(CD) or floppy disk, etc.), such that a device may obtain the variousmethods upon coupling or providing the storage means to the device.Moreover, any other suitable technique for providing the methods andtechniques described herein to a device can be utilized.

It is to be understood that the claims are not limited to the preciseconfiguration and components illustrated above. Various modifications,changes and variations may be made in the arrangement, operation anddetails of the systems, methods and apparatus described herein withoutdeparting from the scope of the claims.

What is claimed is:
 1. A wireless communication device configured forreducing Tx leakage in a receive signal, comprising: a transceiver chip,comprising: a receiver; a feedback receiver; and a transmitter; and a Txleakage signal reduction module, wherein the Tx leakage signal reductionmodule reuses the feedback receiver.
 2. The wireless communicationdevice of claim 1, wherein the Tx leakage signal reduction modulecomprises a notch filter that reduces Tx leakage in the receive signal.3. The wireless communication device of claim 2, wherein the notchfilter is located on the transceiver chip, and wherein the notch filteris coupled to an output of a low noise amplifier that receives thereceive signal.
 4. The wireless communication device of claim 2, whereinthe notch filter is located off the transceiver chip, wherein the notchfilter receives the receive signal, and wherein an output of the notchfilter is coupled to an input of a low noise amplifier on thetransceiver chip.
 5. The wireless communication device of claim 1,wherein the receiver provides a feedback signal to the feedbackreceiver, and wherein the feedback receiver provides a digital leakagereduction signal to the Tx leakage signal reduction module.
 6. Thewireless communication device of claim 5, wherein the digital leakagereduction signal tunes a notch filter in the Tx leakage signal reductionmodule to minimize Tx leakage in the receive signal.
 7. The wirelesscommunication device of claim 6, wherein the notch filter comprises afirst variable capacitor, a second variable capacitor, a first resistor,a second resistor and an inductor.
 8. The wireless communication deviceof claim 6, wherein the notch filter is tuned to provide reliablerejection of Tx leakage across process, voltage and temperature.
 9. Thewireless communication device of claim 5, wherein the digital leakagereduction signal tunes a balancing impedance in a hybrid transformer onthe wireless communication device.
 10. The wireless communication deviceof claim 9, wherein the hybrid transformer comprises a first inductor, asecond inductor and a third inductor, and wherein the balancingimpedance is coupled between the second inductor and ground.
 11. Thewireless communication device of claim 5, wherein the feedback signal isprovided to a feedback downconverter in the feedback receiver by a firstamplifier in a cascode stage in the receiver.
 12. The wirelesscommunication device of claim 11, wherein an output of the feedbackdownconverter is coupled to an analog-to-digital converter via afeedback baseband filter, and wherein an output of the analog-to-digitalconverter is converted to the digital leakage reduction signal by adigital signal processor.
 13. A method for reducing Tx leakage in areceive signal, comprising: receiving the receive signal; processing thereceive signal in a receiver; providing a feedback signal from thereceiver to a feedback downconverter; converting the feedback signal toa digital leakage reduction signal using an analog-to-digital converterand a digital signal processor; and using the digital leakage reductionsignal to reduce Tx leakage in the receive signal.
 14. The method ofclaim 13, further comprising: downconverting the feedback signal usingthe feedback downconverter; and filtering the downconverted feedbacksignal using a feedback baseband filter.
 15. The method of claim 13,wherein processing the receive signal in the receiver comprises passingthe receive signal through a notch filter.
 16. The method of claim 13,wherein the method is performed by a wireless communication devicecomprising: a transceiver chip, comprising: the receiver; a feedbackreceiver; and a transmitter; and a Tx leakage signal reduction module,wherein the Tx leakage signal reduction module reuses the feedbackreceiver.
 17. The method of claim 16, wherein the Tx leakage signalreduction module comprises a notch filter, and further comprisingperforming process tuning on the notch filter using the digital leakagereduction signal.
 18. The method of claim 17, wherein the notch filteris located on the transceiver chip, and wherein the notch filter iscoupled to an output of a low noise amplifier that receives the receivesignal.
 19. The method of claim 17, wherein the notch filter is locatedoff the transceiver chip, wherein the notch filter receives the receivesignal, and wherein an output of the notch filter is coupled to an inputof a low noise amplifier on the transceiver chip.
 20. The method ofclaim 16, wherein the receiver provides the feedback signal to thefeedback receiver, and wherein the feedback receiver provides thedigital leakage reduction signal to the Tx leakage signal reductionmodule.
 21. The method of claim 20, wherein the digital leakagereduction signal tunes a notch filter in the Tx leakage signal reductionmodule to minimize Tx leakage in the receive signal.
 22. The method ofclaim 21, wherein the notch filter comprises a first variable capacitor,a second variable capacitor, a first resistor, a second resistor and aninductor.
 23. The method of claim 22, further comprising: determining ameasured notch frequency of the notch filter; determining a processerror; calculating a first capacitor code and a second capacitor codethat meet requirements for a channel; and applying the first capacitorcode to the first variable capacitor and the second capacitor code tothe second variable capacitor.
 24. The method of claim 23, whereindetermining a measured notch frequency of the notch filter comprises:applying a transmit tone on three different frequencies to the notchfilter; measuring a DC gain through the feedback receiver; calculating agradient; and determining the measured notch frequency using a gradientsearch algorithm.
 25. The method of claim 21, wherein the notch filteris tuned to provide reliable rejection of Tx leakage across process,voltage and temperature.
 26. The method of claim 20, wherein the digitalleakage reduction signal tunes a balancing impedance in a hybridtransformer on the wireless communication device.
 27. The method ofclaim 26, wherein the hybrid transformer comprises a first inductor, asecond inductor and a third inductor, and wherein the balancingimpedance is coupled between the second inductor and ground.
 28. Themethod of claim 20, wherein the feedback signal is provided to afeedback downconverter in the feedback receiver by a first amplifier ina cascode stage in the receiver.
 29. The method of claim 28, wherein anoutput of the feedback downconverter is coupled to an analog-to-digitalconverter via a feedback baseband filter, and wherein an output of theanalog-to-digital converter is provided to a digital signal processorthat outputs the digital leakage reduction signal.
 30. An apparatus forreducing Tx leakage in a receive signal, comprising: means for receivingthe receive signal; means for processing the receive signal in areceiver; means for providing a feedback signal from the receiver to afeedback downconverter; means for converting the feedback signal to adigital leakage reduction signal; and means for using the digitalleakage reduction signal to reduce Tx leakage in the receive signal. 31.The apparatus of claim 30, further comprising: means for downconvertingthe feedback signal; and means for filtering the downconverted feedbacksignal.
 32. The apparatus of claim 30, wherein the means for processingthe receive signal in the receiver comprise means for passing thereceive signal through a notch filter.
 33. The apparatus of claim 30,wherein the apparatus is a wireless communication device comprising: atransceiver chip, comprising: the receiver; a feedback receiver; and atransmitter; and a Tx leakage signal reduction module, wherein the Txleakage signal reduction module reuses the feedback receiver.
 34. Acomputer-program product for reducing Tx leakage in a receive signal,the computer-program product comprising a non-transitorycomputer-readable medium having instructions thereon, the instructionscomprising: code for causing a wireless communication device to receivethe receive signal; code for causing the wireless communication deviceto process the receive signal in a receiver; code for causing thewireless communication device to provide a feedback signal from thereceiver to a feedback downconverter; code for causing the wirelesscommunication device to convert the feedback signal to a digital leakagereduction signal using an analog-to-digital converter and a digitalsignal processor; and code for causing the wireless communication deviceto use the digital leakage reduction signal to reduce Tx leakage in thereceive signal.
 35. The computer-program product of claim 34, whereinthe instructions further comprise: code for causing the wirelesscommunication device to downconvert the feedback signal; and code forcausing the wireless communication device to filter the downconvertedfeedback signal.
 36. The computer-program product of claim 34, whereinthe code for causing the wireless communication device to process thereceive signal in the receiver comprise code for causing the wirelesscommunication device to pass the receive signal through a notch filter.37. The computer-program product of claim 34, wherein the wirelesscommunication device comprises: a transceiver chip, comprising: thereceiver; a feedback receiver; and a transmitter; and a Tx leakagesignal reduction module, wherein the Tx leakage signal reduction modulereuses the feedback receiver.